LONDON—Juan Martin Del Potro says he has been struggling to focus and stay positive since his suitcase was stolen in Paris on Saturday. The Argentine lost a number of personal items, including his rosary that was blessed by Pope Francisco. He defeated Richard Gasquet in his opening match at the ATP World Tour Finals.

“I like to play tennis. I enjoy a lot my work. But someone took some part of my life,” said del Potro, who appeared to tear up during his press conference. “Is really resent, I don't know how you say it. It's tough to don't think about that...One of my things was the rosary. But I have a few things which means a lot from my life. I don't have it anymore."